As is known, the output of a conventional reciprocating piston engine operating on natural gas is about 15% below that of operation on gasoline. This applies substantially throughout the output spectrum of the engine.
When such an internal combustion engine is employed as propulsion engine in a motor vehicle, this differential output deployment is always experienced as disagreeable by the operator when full output is called for, but the engine happens to be running on the fuel of low energy density.
According to DE 195 39 170 A1, it is proposed, to remedy this disadvantage, that the engine be switched automatically to operation on the fuel of higher energy density when high output is demanded, and supplied accordingly.
However, this works only if sufficient fuel of both energy densities is available on board. If the fuel of higher energy density has been consumed, the output deficit cannot be made up by switching to that kind of fuel.